1. Field of the Invention
The present invention relates to a yoke spin valve magnetoresistive (MR) read head and more particularly to a yoke which is employed for carrying a sense current to a spin valve sensor.
2. Description of the Related Art
An anisotropic magnetoresistive (AMR) read head employs an MR stripe which is sandwiched between first and second gap insulation layers which are in turn sandwiched between first and second magnetic shield layers. The MR stripe changes resistance in response to flux from a moving magnetic storage medium which stores recorded data signals. Accordingly, when a sense current is conducted through the MR stripe the change in resistance of the MR stripe changes the potential across the stripe. The potential change is provided as a read back signal. Provision is normally made for longitudinally biasing the MR stripe to promote magnetic stability and for transversely biasing the MR stripe to promote linear response. In order to implement transverse biasing, a pair of magnetostatically coupled MR stripes are normally employed so that when the sense current is passed through both stripes, the stripes bias each other to appropriately rotate their magnetic moments.
The MR stripe is normally located at and forms a part of the head surface which is located immediately adjacent the moving magnetic medium, such as a rotating magnetic disk. Wear of the head surface reduces the height of the stripe, which reduces the strength of the readback signal. Further, leads, which conduct the sense current to the MR stripe, are normally at the head surface, thereby increasing the chance of shorting between the leads and the MR stripe or shorting to the moving magnetic medium. Location of active elements at the head surface also increases the threat to those elements from corrosion.
In order to protect the MR stripe it can be recessed from the head surface by employing a yoke MR read head scheme. The yoke MR read head has first and second yoke portions which are magnetically coupled across an insulative read gap at the head surface and are magnetically coupled at a back gap which is remote from the head surface. An AMR element is located in a break in one of the yoke portions, such as the first yoke portion, intermediate the read gap and the back gap. The distance of the AMR element from the head surface may be on the order of only a few microns. Insulation layers are employed between the AMR element and the first yoke portion to implement a nonconductive magnetic coupling therebetween. The yoke portions, which have the appearance of yoke portions of an inductive write head, serve as a flux guide by transferring flux received at the read gap to the AMR element. With this arrangement first and second leads are connected to the MR stripe of the AMR element for conducting the sense current. An important advantage of the yoke AMR structure is that the trackwidth of the head is not dependent upon the geometry of the recessed AMR element. The width of the yoke portions at the head surface determine trackwidth. Unfortunately, the recessed AMR element has about a 50% signal flux loss compared to a non-recessed AMR element. Therefore there is a strong felt need for an AMR read head which yields the benefits of the AMR structure, without the drawbacks encountered when the active elements are located at the head surface and without the signal loss inherent in the recessed AMR structure.